This invention relates to a fuel injection timing regulator for an engine, and more particularly to a method of detecting the fuel injection timing regulated by such a regulator.
The timing of injection of fuel into the cylinders of an internal combustion engine such as a diesel engine is controlled to be maintained optimum on the basis of the factors including the engine rotation speed and load torque.
For the purpose of optimized control of the fuel injection timing, a fuel injection timing regulator is interposed between a fuel injection pump and the engine driving the fuel injection pump, and the phase angle of the drive shaft of the fuel injection pump under rotation relative to the drive shaft of the engine is properly determined by the function of the fuel injection timing regulator. In a method commonly used hitherto for the purpose of optimized control of the fuel injection timing, a signal indicative of the relative rotation phase angle of the pump drive shaft is fed back for the automatic control of a closed loop circuit. For the purpose of detection of the relative rotation phase angle, a plurality of first rotation angle indicating lugs are fixedly mounted on the circumference, in the direction of rotation, of the engine drive shaft at angular positions corresponding to the upper dead points of the pistons in the respective cylinders of the engine to be sensed by a stationary sensor such as a first electromagnetic pickup disposed at a fixed point, and the length of time required until one of the rotation angle indicating lugs is sensed by the electromagnetic pickup after the preceding one has been sensed by the electromagnetic pickup is measured to provide a reference time. On the other hand, a plurality of second rotation angle indicating lugs corresponding to the first rotation angle indicating lugs are similarly fixedly mounted on the drive shaft of the fuel injection pump to be sensed by another stationary sensor such as a second electromagnetic pickup disposed at another fixed point. The prior art method comprises measuring the difference between the time at which one of the first rotation angle indicating lugs mounted on the drive shaft of the engine is sensed by the first electromagnetic pickup and the time at which the corresponding one of the second rotation angle indicating lugs mounted on the drive shaft of the fuel injection pump is sensed by the second electromagnetic pickup, and calculating the relative rotation phase angle of the pump drive shaft on the basis of the measured time difference above described and the measured reference time representing the length of time required for the engine drive shaft to rotate through the known rotation angle between the angular positions corresponding to the upper dead points.
According to the above method, the relative rotation phase angle of the pump drive shaft can be accurately calculated when the angular velocity of the engine drive shaft does not vary and is maintained constant throughout the period of measurement of the reference time and the period of measurement of the time difference.
However, according to the results of researches and studies made by the inventors, the above condition is not satisfied during the period of warming-up in the starting stage of the engine and during the subsequent initial driving stage, and the engine drive shaft tends to rotate with considerable non-uniformity between one fuel injection timing and the next. Consequently, a large error tends to be included in the calculated value of the relative rotation phase angle of the drive shaft of the fuel injection pump.